I was too. Maybe because I was going for turn 1/2 I found it harder to have enough cards. Also, I don't like the idea of exiling everything but Brain Freeze. I liked to keep some tools I milled through (e.g. Entomb, LED, Pact) to open up more lines of play. For example, what if you wanted to keep Pact open and need fuel for it? And I
never wanted to be in a position where I was forced to exile my 1-of Tendrils because I randomly milled it while digging for Brain Freeze. (Even though you can win without Tendrils, it saved me a lot of effort/time/clicks in sequencing).
Tome Scour might be better than Breakthrough, just digging deeper and letting you keep more cards. Pre-combo you can also cast it to start filling your yard without having to dump your hand. Also, you get bonus lulz for registering
Tome Scour in a sanctioned Legacy tournament.